1. Field of the Invention
The present invention relates to an apparatus and a method for manufacturing toner for use in image forming methods such as electrophotography, electrostatic recording, electrostatic printing, and toner jet recording.
2. Discussion of the Background
Methods of manufacturing toner are broadly divided into pulverization methods and polymerization methods. A typical pulverization method includes a process of pulverizing a kneaded mixture of toner components into toner particles. Pulverization methods are advantageous from the viewpoint of cost. Therefore, toners manufactured by pulverization methods have been widely used for copiers and printers.
More specifically, a typical pulverization method includes processes of mixing, melt-kneading, pulverization, classification, and external treatment. In the mixing process, a binder resin and a colorant, optionally along with a charge controlling agent, a magnetic material, a release agent, and/or a fluidizer, are mixed. The resulting mixture is melted and kneaded in the melt-kneading process, followed by cooling to solidify. The kneaded mixture is pulverized into particles by a pulverizer in the pulverization process. The particles are then classified by size to collect desired-size particles in the classification process. The desired-size particles are mixed with a fluidizer in the external treatment process. Thus, a toner for forming images can be produced.
When the toner thus prepared is used for two-component developing methods, the toner is mixed with a magnetic carrier.
Specific examples of the above pulverizer include collision-type airflow pulverizers and opposed airflow pulverizers (e.g., cutter jet), both of which using jet stream. For example, a collision-type airflow pulverizer is configured to convey a material to be pulverized with a high-pressure gas such as jet stream and inject it from an outlet of an accelerating tube toward a collision member provided facing an aperture surface of the outlet of the accelerating tube. The material is pulverized by the impact force of the collision.
In a case in which a small-size toner is produced using the above collision-type airflow pulverizer, a large amount of air is required and therefore a large amount of electricity is consumed. This is disadvantageous from the viewpoint of energy cost.
Additionally, in a case in which a toner with a volume average particle diameter of 6 μm or less is produced using the above collision-type airflow pulverizer, a material to be pulverized is excessively pulverized and a larger amount of fine particles are produced. The excessive fine particles are required to be removed in a succeeding classification process so as not to degrade classification yield, i.e., toner productivity.
On the other hand, Japanese Patent No. 3870032, Japanese Patent Application Publication No. (hereinafter “JP-A”) 2007-178718, and JP-A 2008-225317 each disclose mechanical pulverizers which are more advantageous than the above-described airflow pulverizers using jet stream from the viewpoint of energy consumption.
A mechanical pulverizer is configured to pulverize a material to be pulverized by introducing it to a circular space formed between a rotor that rotates at high speed and a stator that is disposed surrounding the rotor. Accordingly, the mechanical pulverizer does not require a large amount of air.
Therefore, the mechanical pulverizer consumes an extremely small amount of electricity, which results in drastic energy saving compared to collision-type airflow pulverizers. Additionally, it is unlikely that material to be pulverized is excessively pulverized, which results in enhancement of classification yield. Enhancement of classification yield has been an important issue in the pulverization methods, as disclosed in JP-A 2004-057843.
Focusing on the shapes of toner particles, the collision-type airflow pulverizer produces irregular and angular toner particles, whereas the mechanical pulverizer produces rounded toner particles.
The shape of a toner particle depends on how the toner particle has been pulverized. In airflow pulverizers, pulverization is mostly performed by collision of a material to be pulverized with a collision member. In mechanical pulverizers, pulverization is mostly performed by collision of a material to be pulverized with walls of a stator and a rotor while passing through a narrow gap between the stator and the rotor rotating at high speed. In the latter case, it is likely that pulverization is performed more than once. Also, in the latter case, heat is generated due to the pulverization and the pulverized particles become rounded due to the heat.
In accordance with recent progress in image quality and image definition of copiers and printers, toners are severely demanded to provide better performance. Specifically, toners are demanded to have a smaller size and a narrower size distribution in which no coarse particles and a very small amount of fine particles are included.
To respond to such demands, what is called a closed-circuit pulverization-classification system has been employed in toner manufacturing processes. In the closed-circuit pulverization-classification system, particles which have been pulverized by a mechanical pulverizer are discharged from the pulverizer to a classifier to remove coarse particles, and the remaining particles are returned to the mechanical pulverizer again.
On the other hand, recent toners are small in size for the purpose of enhancing image quality and are including wax components for the purpose of improving fixing performance. Such toners are likely to accumulate within pipings of toner manufacturing equipments, a powder collecting apparatus, etc.
If accumulated toner particles are collapsed on the way of returning of coarse particles to the mechanical pulverizer, the amount of throughput in the mechanical pulverizer may instantaneously increase and therefore the coarse particles may be fed to the classifier. In this case, similarly, the amount of throughput in the classifier may instantaneously increase and therefore the coarse particles may not be returned to the mechanical pulverizer. Consequently, coarse particles may be immixed in the product toner.
Such an instantaneous increase of the amount of throughput in the mechanical pulverizer may make an impact on the inner temperature of the mechanical pulverizer. As a result, pulverization capacity may be unstable and the shape of resulting toner may vary. The accumulation and collapsing of toner particles may also cause interruption or breakdown of the mechanical pulverizer when the toner particles are fixedly adhered to the mechanical pulverizer by increase of the inner temperature.
To avoid accumulation of toner particles in toner manufacturing equipments, vibrators and knockers have been used. Vibrators and knockers can remove partial clogging of toner particles in a toner manufacturing system, however, cannot completely remove accumulation and collapsing in the toner manufacturing system. As a result, the amount of throughput of toner is unstable.
Vibrators and knockers also have concerns that cracks may be generated due to noise of vibration and metallic fatigue.